I bought some lettuce plants at a local garden store a couple of weeks ago and put them in a container. I have put them outside during the day but brought them in at night because it was going below 4 degrees Celsius. The leaves are looking somewhat pale and limp. Should I be bringing the plants in and out or just leaving them outside?

Lettuce is a cool weather crop. I'd leave it outside. If it's limp, my guess is either not enough water, or too much sun. It can stand some afternoon shade. Alternatively, it might be drowning, if it has no drainage...

Just when you learn how to garden really well, you're too old to do it anymore...